The present invention is broadly applicable to a solution and method for electrolytically stripping or removing unwanted metallic deposits or platings from substrates, and more particularly, for stripping unwanted metal plating deposits such as copper, copper alloys, or chromium from electroplating apparatus such as the contact tips of stainless steel work racks, as well as for removing defective or damaged metallic platings from ferrous substrates such as steel in order to enable the stripped articles to be replated without incurring any etching or damage to the steel substrate.
In the art of electroplating, it is conventional practice to support work pieces to be plated on a work rack which is comprised of a chemically resistant metal such as platinumized titanium or stainless steel or a conventional steel work rack having a protective coating thereover such as a polyvinyl chloride plastisol coating. The electrification of the work pieces while suspended in a suitable electrolyte is achieved by stainless steel or platinumized titanium contact tips on the rack which are connected in electrical contact with the work pieces. During an electroplating operation, an unwanted metal deposit builds up on the contact tips of the work rack which interferes with the efficiency and consistency of the electroplating operation. It is common practice, accordingly, to subject such work racks to mechanical or chemical cleaning treatments in order to periodically remove the unwanted metal deposit accumulation in order to maintain optimum operating efficiency thereof.
The stripping or removal of certain metal deposits is also occasionally required from articles which have been electroplated but wherein the resultant electrodeposit or electroless metal deposit is defective or has become mechanically damaged during handling in order to salvage the article and enable a reprocessing thereof. The stripping or removal of the metal deposit from the surfaces of such articles must be performed in a manner which does not materially etch or damage the underlying substrate to a degree which prevents replating thereof and without requiring substantial polishing and/or buffing operations to restore the substrate surface to a condition in which it can be replated.
In the case of stripping metal deposits from electroplating apparatus such as the contact tips of work racks, it is important that the stripping solution and conditions employed do not materially effect an attack of the contact tips themselves causing a progressive errosion of such contact tips thereby reducing the efficiency of the electroplating operation and necessitating frequent reworking and replacement of such contact tips.
A variety of chemical and electrolytic stripping processes and solutions have heretofore been used or proposed for use for removing unwanted metal deposits of various types from substrates including plated articles as well as contact tips of electroplating apparatuses. Typical of such prior art practices and compositions are those disclosed in U.S. Pat. Nos. 2,057,272; 2,578,898; 2,581,490; 2,588,566; 2,596,307; 3,151,049; 3,257,299; 3,492,210; 3,617,456; 3,619,390; 3,649,489; 3,793,172; 3,912,603; 4,048,006; 4,052,254; 4,233,124; 4,244,833; and 4,264,420, to which reference is made for the further details of the processes and the teachings of which are incorporated by reference. A continuing problem associated with many prior art electrolytic stripping formulations and processes has been their inability to effectively strip a wide variety of different metal deposits necessitating separate solutions and processes for the several types of metal deposits to be removed, the relatively slow stripping rate of certain prior art techniques in removing unwanted metal deposits, and the tendency of certain prior art stripping formulations and processes to attack and damage the basis metal during the course of the stripping of the metal deposit therefrom. The present invention may be considered an improvement over U.S. Pat. Nos. 4,233,124 and 4,264,420 as far as the removal of copper, copper alloy, or chromium deposits from ferrous substrates is concerned. As noted above, the teachings of these two patents are incorporated by reference herein. With regard to these last two mentioned patents, it has been found that the elimination of the halogen component, as used in the compositions of these two patents, provides a bath and process capable of stripping relatively thick copper deposits or the like without any build-up of halides on the surface being stripped during the stripping operation. Such a halide build-up in some instances fouls and insulates the surface being stripped, especially in the case of relatively thick metal deposits, i.e., greater than about 1 mil (one thousandth of an inch) up to several inches in thickness. The elimination of the halogen component, however, would not be preferred for stripping metals such as nickel.
The present invention provides for an electrolytic stripping bath and process which is adaptable and particularly suited for rapidly and efficiently stripping relatively thick copper, copper alloy, or chromium deposits from a ferrous basis metal, and which is inhibited so as to significantly reduce the attack and etching of the basis metal during the stripping operation.